Virtualisation
What is Hypervisor?
A hypervisor is the software layer that creates and runs virtual machines, allocating physical CPU, memory and IO between them. A type-1 hypervisor runs directly on the hardware; KVM is unusual in being a type-1 hypervisor implemented as a Linux kernel module, which lets it use the whole Linux driver ecosystem.
Why Hypervisor matters
A type-1 hypervisor runs directly on the hardware; KVM is unusual in being a type-1 hypervisor implemented as a Linux kernel module, which lets it use the whole Linux driver ecosystem.
Hypervisor in practice
When you're running a server on a KVM hypervisor, you look at the actual hardware allocation: vCPUs, RAM, disk I/O. You adjust these from the panel, often hot-adding extra memory without a reboot. Get it wrong by overcommitting the host, and your neighbours' noisy workloads starve your instance's CPU or IO, turning a perfectly configured guest into a sluggish one. Nested virtualisation means you can run a hypervisor inside your hypervisor, handy for testing, but it costs performance and can confuse your own resource counting.
What people get wrong about Hypervisor
The common error is treating the hypervisor as a container boundary. It isn't. A hypervisor gives you a full virtual machine, your own kernel, your own /proc, no shared namespace. People assume their neighbour's processes are invisible or their custom kernel is impossible, then hit limitations. The correction: with KVM, you get genuine isolation and control, so you can boot a hand-rolled image or run nested virtualisation, things a container can't do.
Hypervisor — common questions
What does type-1 hypervisor mean?
A type-1 hypervisor runs directly on the host hardware, not on top of an operating system. KVM is special because it's a type-1 hypervisor implemented as a Linux kernel module, so it can use the whole Linux driver ecosystem for managing hardware. That gives you the performance of bare-metal virtualisation with the flexibility of Linux.
How is KVM different from containers like OpenVZ?
KVM provides true virtualisation: each guest gets its own kernel, its own /proc, and no shared namespace, so you have full root access and can run custom kernels. Containers share the host kernel and namespaces, which limits what you can do. With KVM, you get isolation and control, including the ability to run nested virtualisation or boot a custom ISO.
Where Hypervisor comes up
- Is full-disk encryption useful on a VPS? Against physical seizure of a powered-off disk, decisively yes: the volume is ciphertext without your passphrase. Against an attacker with access to the ru…
- What is your uptime SLA? 99.99% per instance, measured monthly on network and hypervisor availability. Breaches earn automatic service credits on a published scale: 10% below 99.99…
- Can my hosting provider see the files on my VPS? Technically yes: any provider with hypervisor access can read an unencrypted guest disk and its memory. That is true of every virtualisation platform. What…
- What is CPU steal time and why does it matter? Steal time is the percentage of time your virtual CPU was ready to run but the hypervisor gave the physical core to someone else. It appears as the "st" co…
- Is a VPS secure? The isolation is strong: KVM enforces separation in hardware, and escaping it is a serious research-grade exploit. The realistic risk is not the hypervisor…
- Managed vs unmanaged VPS: who patches the server? On an unmanaged VPS the provider guarantees the hardware, the network and the hypervisor; everything above the kernel is yours, including updates, firewall…
More from virtualisation
- KVM
- KVM is full hardware virtualisation built into the Linux kernel, giving each guest its own kernel and hardware-enforced isolation from other tenants.
- OpenVZ
- OpenVZ is container-based virtualisation in which every instance shares the host kernel, so guests cannot load kernel modules or run a different operating system.
- LXC
- LXC is Linux-native containerisation that isolates processes with namespaces and cgroups while sharing the host kernel.
- Nested virtualisation
- Nested virtualisation lets a virtual machine itself run virtual machines, by exposing the processor virtualisation extensions to the guest.
- vCPU
- A vCPU is a virtual processor presented to a guest, backed by scheduling time on a physical core or thread.
- cloud-init
- cloud-init is the standard mechanism for configuring a virtual machine on first boot, using metadata supplied by the platform.